1. Field of the Invention
The present invention relates to a common mode choke coil and a method of manufacturing the same.
2. Description of the Related Art
Known coil components mounted on internal circuits of electronic apparatus such as personal computers and portable telephones include wire-wound types provided by winding a copper wire around a ferrite core, multi-layer types provided by forming a coil conductor pattern on a magnetic sheet made of ferrite etc. and stacking such magnetic sheets one over another, and thin-film types provided by alternately forming insulation films and metal thin-film coil conductors using a thin film forming technique. Recently, there is a rapid trend toward electronic apparatus having smaller sizes and higher performance, which has resulted in strong demand for coil components having smaller sizes and higher performance. Referring to thin-film type coil components, coil components of a chip size of 1 mm or less are supplied to the market by providing coil conductors having smaller thickness.
Coil components include common mode choke coils for suppressing a common mode current which can cause electromagnetic interference in a balanced transmission system and inductors which are combined with a capacitor to provide a low-pass filter (LPF). Patent Document 1 discloses a thin-film type common mode choke coil having an insulation layer and a spiral coil conductor formed using a thin film forming technique between a pair of magnetic substrates disposed opposite to each other. Patent Documents 2 and 3 disclose thin-film type inductors and methods of manufacturing the same. Patent Document 4 discloses a thin-film type micro-coil having a core and a method of manufacturing the same.
Patent Document 1: Japanese Patent No. 3601619
Patent Document 2: U.S. Pat. No. 6,008,102
Patent Document 3: U.S. Pat. No. 5,372,967
Patent Document 4: U.S. Pat. No. 6,876,285
Further size reduction of common mode choke coils is still required. However, in the case of the common mode choke coil according to the related art disclosed in Patent Document 1, it is required to increase the number of turns of the coil conductor to improve electrical characteristics such as impedance characteristics, for example. As a result, the coil conductor must be formed in a larger area, and a problem arises in that it will be difficult to reduce the size of the common mode choke coil.
Further, since the common mode choke coil according to the related art has a pair of magnetic substrates disposed opposite to each other, there is a problem in that it is difficult to provide the choke coil with a low profile.
The common mode choke coil according to the related art is completed through a thin film forming step for forming an insulation layer and a coil conductor (coil layer) on a magnetic substrate in the form of a wafer using a thin film forming technique such as a photo-process, a substrate combining step for combining the substrate with another magnetic substrate by bonding them using a bonding layer formed on the insulation layer, a cutting step for cutting the wafer to divide it into chips, and an external electrode forming step for forming an external electrode. As thus described, the manufacture of a common mode choke coil involves a plurality of manufacturing steps and therefore requires a high manufacturing cost, which results in a problem in that the cost of the common mode choke coil is increased.